The present invention relates to a laser marking hologram and a hologram-oriented laser marking method, and particularly to a hologram excellent in security and a method for obtaining such a hologram, the hologram having individualized information additionally recorded therein such as information of character, numerical character, picture pattern, biometric matter (fingerprint, face, blood vessel, and the like) and/or the like by irradiating laser light to a volume hologram thereby modifying the same.
Recently, attention has been directed to a laser engraving method for directly engraving personal information into a card or the like. The laser engraving technique effectively contributes to constructing a model of a reliable society system improved in safety and durability concerning prevention of alteration and/or falsification of a card face. It marks personal information, face photograph or the like deeply into an inside of a card by engraving based on a property change of a card material itself to thereby complicate counterfeiting, alteration and the like, thereby enabling realization of a high level security in conjunction with various IC card systems.
Meanwhile, the present applicant has developed and placed on the market, a volume hologram transfer foil capable of realizing a high level security by transferring a volume hologram, which is apparent concerning an original or imitation at a glance, onto a card. Such a hologram is mass-produced at a high-speed with an identical picture pattern, by using a hologram master, laser for recording, a hologram photosensitive material, and the like.
On the other hand, it has been known, in a relief hologram having a reflective layer on a backside, to apply marking to the hologram by selectively irradiating laser light to break the reflective layer, from a Patent Document 1, Patent Document 2 and the like:
[Patent Document 1]
JP-A-11-305667
[Patent Document 2]
JP-A-2002-29185
[Patent Document 3]
JP-A-61-72748
[Patent Document 4]
JP-A-2001-96913
It is typical to modify a card surface layer by an optical processing technique such as using laser light, thereby writing personal information by a black/white contrast. However, it is impossible to cause the card to have visible security by this technique only, because it is difficult to distinguish the written information from those recorded by printing, ink jet and the like at a glance.
On the other hand, while volume holograms are produced by the above-mentioned mass-production scheme, it has been difficult to record individualized information since they have no reflective layers like those of relief holograms. Further, even when a method for recording some personal information is realized in a mass-production process such as based on projection or drawing by laser light, ultraviolet light, white light or the like, it will be impossible to attain an excellent quality in all mass-produced products due to a yield ratio thereof.
Moreover, since mass-produced products including media or carriers and holograms, respectively, each have the same picture pattern in the hologram, it becomes impossible to distinguish a true product from a counterfeit one because a hologram of one product can be detached by some way from a medium of the same product and then redeployed onto a medium of another product.